Identification of epidermal growth factor mRNA-expressing cells in the mouse anterior pituitary

Emerging Role of USP8, HMGA, and Non-Coding RNAs in Pituitary Tumorigenesis

Two novel molecular mechanisms with a driver role in pituitary tumorigenesis have been recently identified. They are (a) mutations in the Ubiquitin-Specific Protease 8 (USP8) gene in corticotroph tumors and (b) overexpression of the HMGA1 and HMGA2 genes in most of the pituitary tumors. Moreover, deregulated expression of the non-coding RNAs has been very frequently observed in this neoplasia. The aim of this review is to better elucidate the role, the mechanisms, and the possible clinical impact of these novel alterations in the development of pituitary neoplasia.

Inhibition of epidermal growth factor receptor stimulates prolactin expression in primary culture of the mouse pituitary gland

The roles of epidermal growth factor (EGF) in the regulation of prolactin (PRL) gene expression in the normal pituitary gland remain poorly understood. In the present study, the effects of EGF and an inhibitor of the EGF receptor, erlotinib, on PRL gene expression were examined both in the pituitary tumour cell line GH3 and in a primary culture of the mouse pituitary gland under similar experimental conditions. The results showed that EGF stimulated PRL expression in GH3 cells, but not in normal cells. Erlotinib was found to counteract EGF in GH3 cells inhibiting the PRL expression enhanced by EGF. By contrast, erlotinib induced an elevation in the PRL mRNA levels in the primary culture of the adult pituitary gland and the initiation of PRL production in the culture of the foetal pituitary gland in which PRL production had not yet occurred. Western blot analyses showed that EGF induced and erlotinib inhibited the activation of extracellular regulated protein kinase equally in GH3 and normal cells. These results suggest that the consequences of EGF receptor activation in normal PRL cells contradict those in adenomatous PRL cells.

Genetics of Cushing's disease: an update

INTRODUCTION

Cushing's disease (CD) results from uncontrolled hypercortisolism induced by ACTH-secreting corticotroph adenomas; accordingly, patients diagnosed with CD usually present several comorbidities and an increased risk of mortality. Hypothesis-driven screenings have led to identification of rare alterations in a low number of patients, although the genetic basis underlying CD has remained unclear until recently. Using whole-exome sequencing, recurrent mutations have been reported in the gene coding for the ubiquitin-specific protease 8 (USP8), a protein with deubiquitinase (DUB) activity that modulates the lysosomal turnover of the EGF receptor (EGFR) and other membrane proteins.

METHODS

In this review, we summarize the recent genetic findings and discuss the clinical and pathological implications of USP8 deregulation in corticotroph adenomas.

CONCLUSIONS

Mutations in USP8 have been identified in 35-62 % of functional sporadic corticotroph adenomas causing Cushing's disease, but not in any other type of pituitary tumor. These mutations are found mostly in adult female patients and lead to an aberrant DUB activation by impairing the regulation of USP8 by members of the 14-3-3 family of proteins. The consequence of this hyperactivation is a longer retention of EGFR at the plasma membrane which promotes an enhanced production of ACTH.

Decoding the genetic basis of Cushing's disease: USP8 in the spotlight

Cushing's disease (CD) arises from pituitary-dependent glucocorticoid excess due to an ACTH-secreting corticotroph tumor. Genetic hits in oncogenes and tumor suppressor genes that afflict other pituitary tumor subtypes are not found in corticotrophinomas. Recently, a somatic mutational hotspot was found in up to half of corticotrophinomas in the USP8 gene that encodes a protein that impairs the downregulation of the epidermal growth factor receptor (EGFR) and enables its constitutive signaling. EGF is an important regulator of corticotroph function and its receptor is highly expressed in Cushing's pituitary tumors, where it leads to increased ACTH synthesis in vitro and in vivo. The mutational hotspot found in corticotrophinomas hyper-activates USP8, enabling it to rescue EGFR from lysosomal degradation and ensure its stimulatory signaling. This review presents new developments in the study of the genetics of CD and focuses on the USP8-EGFR system as trigger and target of corticotroph tumorigenesis.

Central role of the EGF receptor in neurometabolic aging

A strong connection between neuronal and metabolic health has been revealed in recent years. It appears that both normal and pathophysiological aging, as well as neurodegenerative disorders, are all profoundly influenced by this "neurometabolic" interface, that is, communication between the brain and metabolic organs. An important aspect of this "neurometabolic" axis that needs to be investigated involves an elucidation of molecular factors that knit these two functional signaling domains, neuronal and metabolic, together. This paper attempts to identify and discuss a potential keystone signaling factor in this "neurometabolic" axis, that is, the epidermal growth factor receptor (EGFR). The EGFR has been previously demonstrated to act as a signaling nexus for many ligand signaling modalities and cellular stressors, for example, radiation and oxidative radicals, linked to aging and degeneration. The EGFR is expressed in a wide variety of cells/tissues that pertain to the coordinated regulation of neurometabolic activity. EGFR signaling has been highlighted directly or indirectly in a spectrum of neurometabolic conditions, for example, metabolic syndrome, diabetes, Alzheimer's disease, cancer, and cardiorespiratory function. Understanding the positioning of the EGFR within the neurometabolic domain will enhance our appreciation of the ability of this receptor system to underpin highly complex physiological paradigms such as aging and neurodegeneration.

Expression and function of ErbB receptors and ligands in the pituitary

The role of ErbB family in discreet pituitary functions is reviewed. Several ErbB receptor ligands, EGF, TGFα, and heregulin are differentially expressed in normal gonadotroph and lacto-somatotroph lineages, and other elements of the anterior pituitary. ErbB receptors, i.e. EGFR and ErbB2, are also localized to the anterior pituitary with preferential EGFR lactosomatotroph expression. EGF regulates CRH and ACTH secretion and corticotroph proliferation as well as exhibiting autocrine and paracrine effects on gonadotrophs and on lactosomatotroph proliferation, gene and protein expression, and hormonal secretion. EGF and EGFR are expressed in both functioning and non-functioning pituitary adenomas, with higher expression in more aggressive tumor subtypes. ErbB2 receptor is detected in all tumor subtypes, particularly in invasive tumors. ErbB tyrosine kinase inhibitors regulate hormonal secretion, cell morphology, and proliferation in lacto-somatotroph tumors, reflecting the emerging application of targeted pituitary therapeutics.

CCR3 monoclonal antibody inhibits airway eosinophilic inflammation and mucus overproduction in a mouse model of asthma

AIM

To explore the effect of a rat anti-mouse CC-chemokine receptor-3 (CCR3) monoclonal antibody (CCR3 mAb) on airway eosinophilia and mucus overproduction in asthmatic mice.

METHODS

An asthma model was sensitized and challenged by ovalbumin (OVA) in male C57BL/6 mice. Asthmatic mice were given dual administration (intraperitoneal injection and aerosol inhalation) of CCR3 mAb or nonspecific rat IgG (ns-IgG). The number of total and differential inflammatory cells in the bronchial alveolar lavage fluid (BALF) was counted. Eosinophils number, the goblet cell percentage (GCP) and airway mucus index (AMI) were measured in the lung tissues. Interleukin (IL)-5 levels in the BALF were examined. The expression of MUC5AC and the epidermal growth factor receptor (EGFR) mRNA in the lung tissues was detected by semi-quantitative RT-PCR. The results were compared among the groups.

RESULTS

CCR3 mAb significantly suppressed the increased eosinophils in the BALF and lung tissues in OVA-challenged mice compared with ns-IgG-treated mice. IL-5 levels in the BALF in CCR3 mAb and ns-IgG administration mice exhibited no obvious changes relative to OVA-challenged asthmatic mice. CCR3 mAb reduced the increased GCP and AMI after OVA challenge and decreased the enhanced expression of MUC5AC and EGFR mRNA in lung tissues in asthmatic animals.

CONCLUSION

CCR3 mAb can significantly inhibit airway eosinophilia and mucus overproduction in asthmatic mice. Blockage of CCR3 may represent a new strategy to asthma therapy.

Active antimetastatic immunotherapy in Lewis lung carcinoma with self EGFR extracellular domain protein in VSSP adjuvant

The epidermal growth factor receptor (EGFR) plays a central role in regulating neoplastic processes. The EGFR overexpression in many human epithelial tumors has been correlated with disease progression and bad prognosis. Passive EGFR-directed immunotherapy, but not active specific approaches, has already been introduced in medical oncology practice. Then we wonder if mice immunization with the extracellular domain of murine EGFR (mEGFR-ECD) in adjuvants can circumvent tolerance to self EGFR, by inducing an immune response with consequent antitumor effect. The present study demonstrated that despite mEGFR expression in thymus, strong DTH response was induced by inoculation of mice with the mEGFR-ECD. This self-immunization, using both CFA and very small sized proteoliposomes from Neisseria meningitidis (VSSP), promoted highly specific IgG titers, predominantly IgG2a and IgG2b. Sera from mice immunized with mEGFR-ECD/VSSP not only recognized EGFR+ tumor cell lines by FACS, but also inhibited their in vitro growth, even in the absence of complement. Noteworthy, vaccination of mice with mEGFR-ECD/VSSP stimulated a potent antimetastatic effect in the EGFR+ Lewis lung carcinoma model, while reproduction-associated side effects were absent. Curiously, mice immunized with the human EGFR-ECD (Her1-ECD) in VSSP though induced highly specific IgG antibodies with strong in vitro cytotoxic effect over EGFR+ human cell lines, showed low cross-reactivity with the mEGFR-ECD. These results further encouraged the development of the Her1-ECD/VSSP vaccine project for patients with EGFR+ tumors.

Ultrastructural immunolocalization of IGF-1 and insulin receptors in rat pituitary culture: evidence of a functional interaction between gonadotroph and lactotroph cells

We have investigated the expression of receptors for insulin and insulin-like growth factor 1 (IGF-1) in rat pituitary cells in vitro and examined the morphological and proliferative changes induced in adenohypophyseal cells by insulin and IGF-1. The proliferation of lactotrophs was determined by double-immunostaining for bromodeoxyuridine and prolactin. Incubation with insulin (10, 100 or 1000 ng/ml) or IGF-1 (5, 30 or 100 ng/ml) for 48 or 72 h significantly increased the number of lactotrophs undergoing mitosis. Co-incubation of insulin or IGF-1 with genistein (25 microM), an inhibitor of the tyrosine kinase receptor, reduced the proliferation of lactotrophs elicited by the hormone and the growth factor. The receptors for insulin and IGF-1 were localized in intact pituitary cells by ultrastructural immunocytochemistry with the colloidal gold-protein A technique. Gonadotrophs expressed both receptors, specific labelling being restricted to this cell type. Electron-microscopical observations of pituitary cell cultures incubated with insulin or IGF-1 revealed gonadotroph cells exhibiting the fine-structural features of enhanced protein synthetic activity. These findings suggest that both insulin and IGF-1 are able to induce the proliferation of lactotrophs through an indirect mechanism mediated by a factor synthesized by gonadotroph cells, in addition to stimulating the biosynthetic activity of the gonadotroph in a direct manner.

Role of extracellular matrix-cell interaction and epidermal growth factor (EGF) on EGF-receptors and actin cytoskeleton arrangement in infantile pituitary cells

Epidermal growth factor (EGF) induces changes in cell morphology, actin cytoskeleton, and adhesion processes in cultured infantile pituitary cells. The extracellular matrix, through integrin engagement, collaborates with growth factors in cell signaling. We have examined the participation of collagen I/III and collagen plus fibronectin in the EGF response of infantile pituitary cells with respect to their cell morphology and actin cytoskeleton. As a comparison, we have used poly-lysine as a substrate. Infantile cells elicit the EGF response when they are associated with extracellular matrix proteins, but no response can be obtained with poly-lysine as the substrate. Cells acquire a flattened shape and organize their actin filaments and vinculin as in focal adhesions. Because the EGF receptor (EGFR) is linked to the actin cytoskeleton in other cells structuring a microdomain in cell signaling, we have investigated this association and substrate adhesion participation in infantile pituitary cells. The proportion of EGFR associated with the actin cytoskeleton is approximately 31%; no difference has been observed between the substrates used. Cells in suspension show actin-associated EGFR, suggesting an association independent of cell adhesion. However, no colocalization of EGFRs with actin fibers has been observed, suggesting an indirect association. Compared with beta(1)-integrin, which is linked to actin fibers through structural proteins, EGFR binds more strongly with the actin cytoskeleton. This study thus shows cell adhesion dependence on the EGF effect in the actin cytoskeleton arrangement; this is probably favored by the actin fiber/EGFR association that facilitates the cell signaling pathways for actin cytoskeleton organization in infantile pituitary cells.

Alpha-melanocyte-stimulating hormone stimulates prolactin secretion through melanocortin-3 receptors expressed in mammotropes in the mouse pituitary

The intermediate lobe of rodent pituitaries is involved in the regulation of prolactin (PRL) secretion from the anterior lobe. In a previous study, we demonstrated the stimulatory effect of alpha-melanocyte-stimulating hormone (alpha-MSH) on PRL release and the expression of melanocortin-3 receptors (MC3-Rs) in cultured mouse pituitary cells. The aim of the present study was to clarify whether alpha-MSH directly stimulates PRL release through the MC3-Rs by determining the cell type of MC3-R-expressing cells in the mouse pituitary anterior lobe. Northern blot analysis revealed a 2.7-kb transcript for MC3-R mRNA in the anterior and neurointermediate lobes of pituitary glands of adult male and female mice. Dual cellular localization of MC3-R mRNA and PRL or growth hormone (GH) in the mouse pituitary glands was performed by in situ hybridization analysis of MC3-R mRNA followed by immunocytochemical detection of PRL or GH. MC3-R mRNA was detected in most mammotropes and some somatotropes. alpha-MSH increased PRL release and stimulated DNA replication in mammotropes, and these effects were blocked by SHU9119, an antagonist of MC3-R and MC4-R. These results indicate that alpha-MSH stimulates PRL release and proliferation of mammotropes through MC3-Rs, and suggest that alpha-MSH from intermediate lobes can regulate mammotrope functions in the mouse pituitary.

Paracrine control of lactotrope proliferation and differentiation

Lactotropes in the pituitary gland might be useful models of how a cell type develops, differentiates, proliferates and regresses under the control of paracrine and autocrine signals. Lactotrope development during embryonic life is determined by a well-defined sequence of temporal and positional actions of locally produced members of the bone morphogenetic protein, hedgehog and fibroblast growth factor families. Transforming growth factor alpha (TGF-alpha), TGF-beta and galanin mediate the action of estrogen on the postnatal expansion of the lactotrope cell population and expression of the gene encoding prolactin in an autocrine/paracrine manner. Moreover, the classic hormone precursor pro-opiomelanocortin generates differentially glycosylated isoforms of its N-terminal fragment as paracrine controllers, which each induce distinct aspects of lactotrope differentiation and growth.

Molecular defects in the pathogenesis of pituitary tumours

The majority of pituitary adenomas are trophically stable and change relatively little in size over many years. A comparatively small proportion behave more aggressively and come to clinical attention through inappropriate hormone secretion or adverse effects on surrounding structures. True malignant behaviour with metastatic spread is very atypical. Pituitary adenomas that come to surgery are predominantly monoclonal in origin and roughly half are aneuploid, indicating either ongoing genetic instability or transition through a period of genetic instability at some time during their development. Few are associated with the classical mechanisms of tumour formation but it is generally believed that the majority harbour quantitative if not qualitative differences in molecular composition compared to the normal pituitary. Despite their prevalence and the ready availability of biopsy material, at the present time, the precise molecular pathogenesis of the majority of pituitary adenomas remains unclear. This review summarizes current thinking.

Epidermal growth factor induces an increase in cell adhesion and an arrangement of actin skeleton in stress fibres in pituitary cultured cells from infantile rats but not adult rats

The rat anterior pituitary gland undergoes changes in its cyto-architecture during the second and third weeks of postnatal life. However, little is known about the factors that regulate these tissue conformational changes. The epidermal growth factor (EGF) is one of the growth factors that are synthesized by the pituitary gland, and almost all of the pituitary cells have EGF receptors (EGFR). In addition to the effects of the EGF on mitosis and differentiation, this growth factor can modulate cell adhesion, cell migration, and cytoskeletal organization. In this study we focussed our attention in examining the effects of EGF on the adhesion of cells to the extracellular matrix and on the actin cytoskeletal arrangement of pituitary cells from infantile and adult rats. Our results show that in infantile cells the EGF induces cell adhesion with increase in cell surface area. The arrangement of actin-F in infantile EGF-treated cells was in stress fibers and vinculin acquired a striped shape at the membrane border, suggesting the assembly of focal adhesion contacts. In contrast, in adult pituitary cells EGF does not induce any change in cell adhesion, and the cells maintain a rounded shape with an arrangement of actin-F in thin cortical bands even though, immuno-localization of the EGFR was observed in adult cells cultured in defined medium. We also looked for the EGFR in membrane preparations from infantile and adult pituitaries, and a marked difference in membrane EGFR was observed between them, the infantile pituitaries showing a significantly higher amount. Our results suggest that in infantile cells EGF induces the assembly of focal adhesion contacts, and that in adult cells the receptor of this growth factor is uncoupled of the signaling pathway by which a rearrangement of actin cytoskeleton occurs.

Mitogen-activated protein kinase mediates epidermal growth factor-induced morphogenesis in pituitary GH3 cells

Epidermal growth factor (EGF) causes pituitary GH3 cells to change from their normal predominantly rounded morphology to much more elongated cells with extensive filopodia, and this effect is accompanied by a parallel increase in cell volume. In view of this, and because EGF receptor expression is increased in some pituitary tumours, we examined the mechanism of this EGF-induced morphological effect as it may play a role in tumour invasiveness. The effect of treatment of the cells with EGF (1 nm, 4 days) was determined visually (expressed as percent non round cells) and by measuring the cell volume by Coulter Counter analysis. EGF treatment caused the cells to change their morphology with percent non round cells increasing from 37% in control cells to 74% in EGF-treated cultures; this was accompanied by a parallel increase in cell volume. Treatment of the cells with EGF in the presence of the MEK1 inhibitor (PD98059) completely blocked the EGF-induced morphological changes, showing that activation of the mitogen-activated protein kinase (MAPK) pathway is necessary to mediate this effect. Transfection of the cells with a constitutively activated mutant of MEK1 produced a similar morphological change to that produced by EGF treatment, with the proportion of non round cells increasing to 62% with a parallel increase in cell volume compared to cells transfected with the empty vector, demonstrating that direct activation of MAPK pathway is sufficient to mediate the observed morphological effects. The effects produced by activated MEK1 transfection could be blocked by PD98059. EGF had opposing effects on prolactin and growth hormone (GH) secretion by the cells, increasing prolactin release and inhibiting GH release. Transfection of the cells with activated MEK1 produced similar effects on hormone release as EGF treatment. In conclusion, the morphological effects of EGF on GH3 cells are mediated by activation of the MAPK pathway as blockade of this pathway abolished the observed effect, and direct activation of this pathway by transfection with an activated mutant of MEK1 was able to duplicate these effects. This mechanism may contribute to the growth and possibly local invasiveness of some pituitary tumours that express the EGF receptor.

Intrapituitary regulatory system of mammotrophs in the mouse

Estrogen stimulates the proliferation of pituitary cells, in particular mammotrophs. The present study was designed to clarify involvement of transforming growth factor alpha (TGF-alpha) in the estrogen-induced growth of mouse pituitary cells in vitro. Anterior pituitary cells obtained from ICR male mice were cultured in a primary, serum-free culture system. Proliferation of pituitary cells was detected by monitoring the cellular uptake of a thymidine analogue, bromodeoxyuridine. Secretory cell types were immunocytochemically determined. Treatment with TGF-alpha (0.1 and 1 ng/ml) for 5 days stimulated cell proliferation. Since TGF-alpha binds to the epidermal growth factor (EGF)-receptor, this action may be exerted through this receptor. Estradiol-17beta (E2, 10(-9) M) stimulated proliferation of mammotrophs. RG-13022, an EGF receptor inhibitor, reduced the cell proliferation induced by EGF or E2, showing that the EGF receptor was involved in this induction of mammotroph growth. Treatment with TGF-alpha antisense oligodeoxynucleotide (ODN) inhibited the cell proliferation induced by E2, but treatment with EGF antisense ODN did not. Dual detection of TGF-alpha mRNA and growth hormone by in situ hybridization and fluorescence-immunocytochemistry demonstrated that TGF-alpha mRNA was detected in most somatotrophs. Our recent RT-PCR analysis revealed that E2 stimulated TGF-alpha-mRNA and EGF-receptor mRNA expression. These results indicate that TGF-alpha produced in somatotrophs mediates the stimulatory effect of estrogen on pituitary cell proliferation in a paracrine manner, and that EGF-receptor expression is stimulated by estrogen. These findings indicate that intrapituitary cell-to-cell interaction plays an important role in the control of pituitary secretory cells.